The invention relates to a method for producing a foil of synthetic material composed of a first synthetic compound and a second synthetic compound, in which the first synthetic compound consists of a polymer and the second synthetic compound consists of a plastomer.
The invention also relates to a synthetic fibre and to an artificial lawn suitable for sports fields, consisting of a substrate to which synthetic fibres according to the invention are fixed.
A synthetic material having the composition according to the above introduction is generally known, in the form of a foil it is widely used as a packaging material or a roofing material. Synthetic materials are currently being used for all kinds of purposes, and significant developments in particular as regards the use of all kinds of synthetic materials in artificial lawns for sports fields have been realised the past few years.
In this connection, research has in particular been concentrated on the development of synthetic fibres for use in artificial lawns for sports fields, in which fibres of a particular length are fixed to a substrate, for example by tufting. The development of artificial grass fibres and artificial grass sports fields derived therefrom has progress so far that it is possible at present to construct artificial grass sports fields which are very difficult to distinguish from natural grass sports fields, not only as regards the way it looks but In particular as regards the way it behaves during play.
Unlike natural grass sports fields, artificial grass sports fields can be played on longer and more intensively, irrespective of the weather conditions. Currently, the development of new artificial grass fibres is in particular focussed on obtaining a fibre which will further reduce the number of injuries, such as grazes and burns when making slidings, or the incidence of twisted joints.
Existing fibres which have been specifically developed for artificial grass sports fields have this drawback, however, that they are more prone to splitting in the longitudinal direction after being stretched in that direction. Such a fibre will thus split sooner, for example as a result of being played on, which makes the fibre less suitable for use in an artificial grass sports field. The split parts of the fibre will break off sooner, as a result of which matted or otherwise bare, intensively played-on patches will form in the artificial grass sports field. This has a very negative influence on the playing properties of the artificial lawn, such as shock absorption, sliding resistance, grip and water permeability, which in turn increases the risk of injury.
It has become apparent that when the synthetic material as referred to in the introduction is in accordance with the invention extruded into a synthetic fibre, said fibre is quite suitable for use in an artificial grass sports field. The fact is that it has been established by experiment that a suitable selection of the composition or the proportion between the first synthetic compound and the second synthetic compound leads to a synthetic fibre having mechanical properties such that, due to the specific molecular structure, the fibre will split much less easily in the longitudinal direction.
This renders the fibre ideally suitable for use in an artificial grass sports field.
According to the invention, the splitting behaviour of the synthetic fibre can furthermore be significantly improved by stretching the fibre after the extrusion process. Apart form an increase in length, according to the invention the selection of materials after the stretching process gives the fibre its strength in transverse direction, as a result of which it will split less easily. When used in an artificial grass sports fields, such a fibre, and consequently the artificial lawn, will have a much longer life, the artificial lawn will require much less maintenance and will thus remain playable longer. Furthermore, the risk of injury of the players is considerably reduced.
According to the invention, the fibre may consist of at least one monofilament, in which case the fibre may be twined into a strand of several monofilaments.
On the other hand, the fibre may according to the invention be formed as a band, and more in particular as a fibrillated band fibre.
According to the invention, a fibre having a very advantageous non-splitting behaviour can be obtained in that the proportion of the plastomer in the fibre is 30-80 wt. %, and more in particular 35-50 wt. %.
The first polymer may be polypropylene or polyethylene, and in particular (linear) low-density polyethylene, high-density polyethylene, homo-polymer polypropylene or copolymer polypropylene.